[TDF9]

I'm in the middle of a front end rebuild that has become far bigger than I'd intended. One result is i now have the steering knuckle out - only way to get the #@!#$! ball joint out - and have wire wheeled off 15 years of new England rust. Hate to see it immediately succomb to the rust monster again. Is there any reasonable way to slow or prevent the return of the rust on the knuckle? Some sort of coating or wax? I appreciate any thoughts!

[Ohio Enthusiast]

Fluid Film. One spray can will cover all fasteners and control arms, but you'll need more if you want to cover subframe/rails/etc. There are many other products that do the same. You need an oily product that doesn't attract dust. Stay away from rubberized undercoatings - they work great until they are compromised by road debris, then they trap moisture and accelerate rusting.

[Yngvejos]

+1 on Fluid film I treated my E87 with it 3 years ago and it have protected it well.
I had brand new Bilstein shocks and Eibach springs when applied the fluid film these still look brand new if I wipe away the grease.
As an extra bonus, it loosens rust on nuts and bolts so stuck suspension bolts are no longer a problem.

[BMW Guy]

I thought BMWs came with rust protection from the factory in the form of oil leaks.

[jsunma]

Originally Posted by BMW Guy

I thought BMWs came with rust protection from the factory in the form of oil leaks.

Exactly...that's my experience.

I think Fluid Film is fine, but is pretty light weight stuff. I've used it on my old cars, and while I don't think it does any harm, I also don't think it does much at all. At least not in a New England/Canadian driving environment.

If you're really serious about this - kudos to you if you are - I would recommend one of those commercial oil spray services. Perhaps a Canadian can chime in as I believe that these things are common up there. I've used a domestic US alternative (https://nhoilundercoating.com/) and when done properly, it's an amazing thing. It's pretty much based on the same stuff as Fluid Film, although it's Fluid Film on steroids. It's a thick, gloppy, undercoating that smells and drips off your car for weeks...but it effectively seals out the water and hence rust.

Two caveats. One, the process has to be done properly, and the company I noted above unfortunately franchises their process and some will be happy to charge you the $300 it costs without doing a proper job. So, check reviews. Second (two), on our cars (E90 bmws) it will require removing the underbody shields in order to get the stuff everywhere and hence make it worth the price of doing it. To that extent, I've actually NOT done it on my E91, instead preferring to just deal with corrosion on parts such as what you mention (remember, the front subframe is aluminum, so rust isn't an issue...the rear, well, that's an issue). I have done it on my 45 year old Volvo and my 20 year old Toyota with very positive effects. I'm close to pulling off the underbody shields and getting it done on the E91.

[Bims328i]

Silicone, good ol' silicone. Cheapest option. Even on areas like sub frame where there is rust you can spray some silicone there to protect it down the road. Metal corrosion is like a type of scab metal gets and if sprayed or saturated while dry with silicone spray the silicone will soak down into all those little areas. The spray will quickly dry and not leave an oily residue.

I found CRC's heavy duty silicone spray works nice with the little nozzle tip as it is like a mist and doesn't come out in a frothy liquid like PB's silicone spray so it's nice for coating areas without a ton of runoff.

Of course, this has the best effect when the part or area is clean beforehand (or do it to new parts and or vehicles) but it will add a layer of protection.

[3PedalJake]

Your profile says 2006 325i, which doesn't make sense because that has an aluminum knuckle. Are we talking about a xi? The cast iron knuckles are painted, yours probably all rusted off but I'll bet theres a few patches of it left. Having it powder coated is the best solution, but for a DIY painting with some epoxy 2k is your best bet.

[TDF9]

Thanks for all the responses! Will try one of these on the knuckles before I reassemble.

3pedaljake - yes, this is an ix. I still have the 2006 325i, but now added an 08 e91 328xi. So iron knuckle with little sign of original paint left.